Road to Mac OS X Leopard: Time Machine

Time Machine is one of the most visually prominent new features demonstrated in Mac OS X Leopard, even if the core idea of backups is as old — or perhaps older — than the concept of having any data worthy of being restored. Here's a look at what's new and different about Apple's approach with Time Machine, why backups are a problem to be solved, and how well Leopard's new Time Machine actually works in practice.

The Origins of Time Machine

Picking a specific origin of the legacy of Time Machine is more difficult than other new features in Leopard, because it is a combination of old and new technologies. The new Time Machine is a stack of three functional layers:

The new technology behind visualizing backed up data and restoring files.

Its standard and ordinary data backup management functions.

The novel core technologies behind how it squirrels away its archives.

The technologies on the top and bottom of the stack are what is really new and interesting about Time Machine; there's certainly nothing new about performing backups. The problem for most users is that, while they know they should be backing things up, they don't do a very good job of it for a number of reasons. It just so happens that what Apple is adding in Time Machine addresses those reasons, shielding users from the complexity and the tedious backup maintenance that prevents most people from backing up their information properly.

Backup Against the Wall

Data backups, like security measures, are a trade off between safety and convenience. Backing up everything frequently and saving backups over long periods is safe, but it's not very convenient. Doing little or nothing — say, duplicating the project you're working on so you have another version in case it gets corrupted — is convenient but not very safe. The problem for most users is that an all-out data crisis doesn't happen frequently enough, so there isn't much motivation to set up a backup system that is robust enough to work correctly.

The flip side is that some users get a backup system set in place that appears to be working, and are lulled into a false sense of security, unaware that it isn't. The faults might lie with unreliable back backup media, procedures not being carried out correctly, or the system not capturing new data it was not originally designed to protect.

The third problem related to backups is that even when diligent IT professionals take it upon themselves to build systems to backup data securely — all the time, with multiple levels of protection — the result can be extremely expensive, disruptive, and laborious to operate. That's the classic problem of the engineering triangle: balancing the three constrained demands of time, quality, and expense to build something good enough to suit its intended purpose.

Targeting Time, Quality, and Expense

In order to perform effective backups and ensure they will get done, the backup system has to be fast enough, do a good enough job, and not cost too much. It has only been fairly recently that hard drives have become the best way to back up most data.

Tape Backup: In the 80s and 90s, computer users commonly relied on tape drives to supply a fast enough, somewhat reliable, and cheap medium to spool off all their data for backup. Tapes were far more economical than storing data on hard drives and could chug along in the background or at night using automated software. However, it could take a very long time to pull data back off the tape, and physical tape was notorious for wearing out, breaking, or getting too dirty to work.

While tapes were commonly cheap enough, tape backup units are typically quite expensive, particularly among higher end formats that promised better reliability such as the "built like a tank" DLT format. Consumers and smaller businesses more commonly used the less reliable DDS tapes (above).

Diskette Backup: The cheaper alternative to tape was using floppy disks, but common floppies didn't hold much data. In 1983, Iomega introduced the Bernoulli Box, which was popular among Mac users for backing up a whopping 35 MB per disk over a fast SCSI cable. The storage capacity of Bernoulli disks — which were basically heavy duty floppy disks — steadily increased as technology allowed more data to be packed into the disk, peaking out around 230 MB (above). Iomega's arch rival was SyQuest, which sold hard drive platters packed into a removable cartridge. In addition to being used for backups, Bernoulli and SyQuest cartridges were also used for general storage.

Magneto Optical Drives: In the late 80s, magnetic floppies were quickly being outgrown by users, while the technology of mechanical hard drives seemed to be hitting a price-performance barrier. Steve Job's NeXT bet on Canon's new 256 MB Magneto-Optical drive technology for use its new line of computers, hoping that MO drives would be to the NeXT Cube what Sony's 3.5" floppy had been for the Macintosh back at Apple. It turned out that the first-generation of MO drives were unreliable, never dropped dramatically in price, and couldn't match hard drives in performance. The short lived Floptical format and Sony's MiniDisc also used MO technology, but neither took the world by storm and found only limited adoption.

New Disks in the 90s: In 1994, Iomega replaced its Bernoulli Box with the cheap, 100 MB Zip drive (above). It became very popular, eventually being built into many PCs and Macs as a functional replacement for the floppy. SyQuest tried to release its own competitor with the "EZ 135," which offered more space, was significantly faster, and used a more reliable hard drive platter rather than the Zip's heavy duty floppy design, but Zip won out, and Iomega eventually bought up the remains of SyQuest a few years later.

Laser Optical Drives: The next backup medium that caught on among consumers was CD-R, which offered far more storage than the Zip on an extremely cheap medium that kept getting cheaper. CD and DVD media remains cost effective for storing backups of some content today, although modern 500 GB hard drives can quickly fill up 8 GB DVDs. Dual Layer DVD blanks are still fairly expensive, and successive versions of optical disc, including 50 GB recordable Blu-Ray BD-R, are even pricier.

The Internet: By 1998, Job's Apple released the iMac without any floppy disk, a move that stunned the PC industry. How would users write their files? Even ten years later, most desktop PCs still throw in an ancient 3.5" floppy drive. In the decade since, the rewritable CD and DVD have become the new floppy, but the importance of dumping data on a removable disk rapidly waned in a world where nearly everyone was connected by ubiquitous networking. The "I" in iMac was for Internet, and users were supposed to use it to distribute their files.

State of the Backup

In 2007, the idea of backing up data to a tape drive is foreign to anyone outside of a server room, and even enterprise users are increasingly moving to hard drives for many backup purposes. Home users often make casual backups on DVD, or to a network file service, or dump data onto a removable hard drive. The general reliability of hard drives means that we don't face data loss as often as we used to in the days of having files strewn about on magnetically sensitive floppy drives.

Apple's current Backup application (below) is designed primarily to work with .Mac, and works a lot like most other existing backup programs. Users manually select files to be backed up and schedule times for when backups should occur. Backup was intended to copy data to a user's online .Mac account, but can also backup to an iPod or to CD or DVDs.

The problem is that the cheap storage space afforded by today's hard drives means we now have outrageously huge mountains of important data sitting on our disks, so that any failure or error can wipe out far more content than a bad floppy could have back in the 80s. The progress of technology in hard drives' size and economy is not only the problem, but also the solution: duplicate your important data on another hard drive.

On page 2: The Technology Behind Time Machine; The What; The Where; The When; and The How.

I only back up my Home folder so the size isn't that bad. The only thing TIme Machine needs is a reset all button or the option to pick a point to stop backing up, meaning every day my back up has been growing, sooner or later my HD will be filled with stuff I will never need. From the version I'm testing my back up is growing 200mb a day. I need a cut off point. DaJa Vu does a great job of letting the user pick the point where it no longer backs up.

A question for those who have tested it: how large should a typical Time Machine backup drive be? I understand that this will vary with our use etc., but let's assume that I have an iMac with a 320 GB disk, about 100 GB of it available. WHat size drive should I consider for backup? How often do you think I'll need to add another backup drive?

I'm looking for ballpark figures from someone who's used it, if possible. Thanks!

So what happens if my whole system goes down - can I retrieve the situation using Time Machine - will it replace a bootable back-up system like Super Duper?

My guess is no. You would probably need to reinstall the system and then retrieve your files from the backup. However, I guess Time Machine wouldn't work since it looks for files in the same location which it wouldn't be on a fresh install. You will probably need to retrieve them manually. Hopefully, there will be some way to do a mass restore of your backup. But at the very least, I guess you could just copy the files back where they go in the new system.

We use a Tiger server here with Mobile users (so the home directory of each user is backed up on the server).

When we move to Leopard Server (which I hope will ship concurrently with Leopard!), will the user be able to use Time Machine to undo deletions off their home directory from their laptop, with Time machine doing the backups against their synced home directory?

That would be a huge blessing for my IT staff. Anyone know if this will work?

My guess is no. You would probably need to reinstall the system and then retrieve your files from the backup. However, I guess Time Machine wouldn't work since it looks for files in the same location which it wouldn't be on a fresh install. You will probably need to retrieve them manually. Hopefully, there will be some way to do a mass restore of your backup. But at the very least, I guess you could just copy the files back where they go in the new system.

What would be great is if you could boot from the leopard dvd, and run a restore which searches for a time machine backup and lets you do a complete restore back to a specified date.

Tape Backup: In the 80s and 90s, computer users commonly relied on tape drives to supply a fast enough, somewhat reliable, and cheap medium to spool off all their data for backup. Tapes were far more economical than storing data on hard drives and could chug along in the background or at night using automated software. However, it could take a very long time to pull data back off the tape, and physical tape was notorious for wearing out, breaking, or getting too dirty to work.

While tapes were commonly cheap enough, tape backup units are typically quite expensive, particularly among higher end formats that promised better reliability such as the "built like a tank" DLT format. Consumers and smaller businesses more commonly used the less reliable DDS tapes (above).

Do not belittle the tape drive.

For large storage amounts that need to be securely stored (i.e. business use) it is still the most economically feasible solution. Sure HDDs are getting cheaper, but imagine companies that store a TB-sized complete system backup weekly for a 5-year history. The price in HDDs would be astronomical. Tapes are a cheap solution that work, albeit a slower process. There is nothing to date that can sufficiently replace this for businesses.

Granted for home use, no one creates weekly backups and ships them offsite, but the topic should not go without mention, especially as more and more businesses use Macs. Time Machine (or at the very least ZFS formatting) has the potential to save big $$ on redundant backup.